Women entered Leiden University relatively late: The first students arrived in 1878 and the first Ph.D. degree is from 1903 (a thesis in law, by Adolphine Kok). The first four women with a physics Ph.D. all studied theoretical physics, and all four had Hendrik Lorentz as their promotor. This remarkable alignment might be explained by the circumstance that Lorentz's wife, Aletta Lorentz-Kaiser, was deeply involved in the women's rights movement in Leiden.